Apparatus for testing and controlling the concentration of solutions



Oct. 27, 1953 w. N. LINDSAY 2,656,845

APPARATUS FOR TESTING AND CONTROLLING THE CONCENTRATION OF SOLUTIONS Filed March 6, 1948 9 Sheets-Sheet l TII3 1 4 LL n T @&g%@ a @5 1?) INJVENTOR WESLEY IV. LINDSAY B) @W a. W

44W, TTORNEYS Oct. 27, 1953 w. N. LINDSAY 2,656,845

APPARATUS FOR TESTING AND CONTROLLING THE CONCENTRATION OF SOLUTIONS 9 Sheets-Sheet 2 Filed March 6, 1948 INVENTOR WESLEY N. LINDSAY G M4Q a.

ATTORNEYS Oct. 27, 1953 w, UNDSAY 2,656,845

APPARATUS FOR TESTING AND CONTROLLING THE CONCENTRATION OF SOLUTIONS Filed March 6, 1948 9 Sheets-Sheet 3 T'IE'| i?! 22 I 94' l I I I 5/ INVENTOR wsszzr IV. LINDSAY ATTORNEYS Oct. 27, 1953 w. N. LINDSAY 2,656,845 APPARATUS FOR TESTING AND CONTROLLING THE CONCENTRATION OF SOLUTIONS Filed March 6, 1948 9 Sheets-Sheet 4 INVENTOR T. I l3 5 WESLEY M LINDSAY ATTORNEYS Oct. 27, 1953 N LINDSAY 2,656,845

W. APPARATUS FOR TESTING AND CONTROLLING THE CONCENTRATION OF SOLUTIONS Filed March 6, 1948 9 Sheets-Sheet 5 382 v 5 32 w J7 .3

Indicator, Liquid Rnorvoir Trlcfinq Tank ConcQntraM Tank INVENTOR WESLEY N. LII/D51) w @W a M Q'I'TORN EYS I W. N. LINDSAY FOR TES Oct. 27, 1953 TING AND CONTROLLING THE CONCENTRATION OF SOLUTIONS APPARATUS 9 Sheets-Sheet 6 Filed March 6, 1948 INVENTOR WESLEY 1v. LINDSAY ATTORNEYS Oct. 27, 1953 W. N. LINDSAY APPARATUS FOR 2,656,845 TESTING AND CONTROLLING THE CONCENTRATION OF SOLUTIONS Filed March 6, 1948 9 Sheet-Sheet 7 F1|3 Ei FII3 1Z Latch Disabling Mocnaniun Z l Acfuo'ing Lump a Tufinq Pump llIXII'II'VIII!Ill-IIII'I'IIIIIIIITTIIIIII'IIIIIIIII'IIIIIIIIIIIII'III'III] 00 O -OOOOOOO "222:3:2322222333333;-2.2"...

L 0n. Cyclc=3 mmnn i I 7] mveu'roa WESLEY ll. LINDSAY ATTORNEYS Oct. 27, 1953 w. N. LINDSAY 2,656,845

APPARATUS FOR TESTING AND CONTROLLING THE CONCENTRATION OF SOLUTIONS Filed March 6, 1948 9 Sheets-Sheet 8 /Z// Ma Ii g /I 35 62\ 3 1 /Z W784 I i/ 8 a L WM f a ,7 8 L w) M l J 67/ I q o i [35 1 /a0 I I 1 I I /6/ i 2/ 3 f M 20 36 t 2/ T' 1 E: I a

IN VENTOR WESLEY Iv. LINDSAY ATTORNEYS 1953 w. N. LINDSAY 2,656,845

APPARATUS FOR TESTING AND CONTROLLING THE CONCENTRATION OF SOLUTIONS Filed March 6, 1948 9 Sheets-Sheet 9 IOO Hypochloritc Solution Indicator Y Btu. Filtcr b z 860- 2 z in z E R '540 m 0 E] q a.

Blue Filtu Hypochlorit! I Solution +-lndicator 2O R Green Filter WAVELENGTH, MILLIMICRONS a u w p- .-l o

TIME INVENTOR WESLEY IV. LINDSAY BY @W a TTORNEYS -co ol ne th o eeni et q of particular utility in-the treat I sing or retardin the g rovvthpf tieca li wa r tn ai a lio ieu ti r ereql fi I rd yi r e t fru t-o wee ieb zi m the .-;it is of great importance that the germicidal st en t ?.b Qau L -Li h Q 19 14,

er t y de end neii e t en tu es t -.1H i i vi en y n tQ P em-V chy s mpl ife di e; ainewlsupp ytcf th Patented Get; 27, 1953 UNI TED APPARATUS- FQR TE STING AND CONTROL- LING THE (IQNCENTRATION -OF :SOLU- 11 'EIONS wes ley N. Lindsy, San Jose Qalif a s signorto li iei gap hemi a Qomiira ipn; a

of pelaware App icat on Ma -ch 6, Q ,;Ser ial.;N 1346s spr s nt ;-i ve ti pe tai ava s of ol -r n --deavin q 'tec e stopageand shipping peripdsit 's of va ge to treat them with solutions off -su table; ge -"rlriiiq jjal sub,st ances, such, as sod irn hypgchlogite, .o thophen lphen and 19 ci c b ei u u l wa c me by Q0 li qmi throu h. ,a sho 9 e t wle i ui e it e zfr-om a fla dines ev e' an ti r ase efii eeno- .my {t e s r u i uid-d ain n mmsih tn e l is ather d i a. ten -end retume yt i t emedine; evic i rven we u In treating fruitand ve get a:;bles in this rnanner tio eeat:e a m s meintained i h m ii liable toud le eri usl \efi ti text has. 8,

and ppe rance; =..1t., e i edu ta d husimpa its marketability.

, T l nta zt sQl t Q et-ii p e n'si enei during repeated MSG ,-;it is evidently necessary v to a d w; su es o them cid l su stan sa we, the p ed; a d :wntmui fw-tthe s .7 15mmie l n l eexte iie i h whe' eqi ic i s fie y em n ie ab gdi an .-oth

concentrate at; {equal in ry tintol the tank, theausedependin upon any one .Qflthe, abovemem iion f ct r i s eh a. prQceduremiehttrendenthe Ztwa iq id harmiuuyscron ontleaye; it ineft ee ve ewea y x 5 --It is, therefore necessar .toytestlsnecimensi-of ,-'-the sterilizin iliquidk at periodic .inteizvals tot-determine the ,qonc entr ation thereof @ndL-xe ulate the ,coliceiiira e sup l ac ording, to; lthe results t ate .aq rd n e withimy invention this is accomplishedhy bringing;speeimenstoftthe solution; into eontaet with ,an indicatorj 'iiquid fwh s qepie l i l 121 8. i b zli ansmissionlof said solution to anextent cietenminedbyithexelavtiv, tyx f :th e erm i hselutei. contained t e a ns e tin uthe mola -[ed t rqu e li ht-imp icit he oh s e uwhi h ereen ew ab rrat o ,oft-me henismedepb quantiti s, of h emeenfifiefinto; t

- ,20 quid they too quantities helmgew 4 id pend n vupo the, ei i ni to wh t u i n haspwn QlQred, 1 6. changed it s ability of trans- ;ii itt J nt i pgn; Contact w th 7 the ind; gitor fluid.

g lt is an objectpf the invention to provide a sim i s' i e an e ri n 'b e eer l i f --a.ewmei im ie a i th c ri i' le ib vaeolution,Evvitl in pnedetermined-l ts. i

Another objeetis to provide control mechanism, for sterilizing solutions of tthe type de scrihed, whic e adapte o-automat in reas he twneem iiq 9 s ise u i n a een a h relative quantity of the active agent cnnt ned therein drqpsl, below a ;-p edete tmine,d lower limit.

s oth b eiisi tprev id t a p hei ref behav n w en t n lmeehani m e ise e n v he p qlui o an n din em osit ve .;;-Pr n eee sii oxi re ie mechanism.

fu r biecii iiq .m i a a e ie eqan J n r he nqen aii at sqluiio' t iii (type ch raet ze whi ie i' n i -m .u om n suspen its eperaiio v hfe imrv pa t its mechanism becomes defective."

A the l2i i o ii tpro t s s -i ty re rred; llwhi ran e ;i ff etomaie Cally Suspend its QZ'QPiP J-WhQQ Y-H i vsen l i eei l fil $b l1$6 Another object is to provide a system, pf the lt eehet c etiee i wit s nel nemeens acei to Warn qe ei e iendan when v i i' y oiem r lieqe sh li s,q n Q m Ql 0 lated. therewith. l

Fru an ve e abl -;-o i.-he 1veste ta *i i fluently ente 'neie y; rtten ,pihe if zeie ,o o k el-1 by i s e il zi PmfiQn heni e erpdu is ime'ied-i ihei tenfen-ed t e ui o em Jew r i i upon the light beanie-1e hot the indicator lii iiid with the U A a lt. weet-tit e P1 9 1 @Q i s -i n' register ppor transmission ofthe sterilzing representative bfhigh eoncentraitifln and; suspend operation of the concentrate replenishing mechanism at a time when-theconcentiation of the. solution has. dropped below its lower 'pefrnissiblelimit. :uFluctua'tions in the-intensity of' the light emitteqeby; the iamps employed .in photoelectric l eontrol systemspf v the. .type here under qqnsiq ee ip mm ylcausesimil r nisoperatiomof u h sy s andth s re ult int. ecay on destruction og} arge amounts of fruity and .izee'etables.

hete r lenoih n. Objec of-tthemesent nventio iPrQYi e-L a.- m,etho ..ion ascertaining 3 variations in the light absorbing properties of an object which results from processing said object to alter its color, irrespective of Variations in the light absorbing properties of said object in its natural condition.

It is still another object of the present invention to provide a photo-electric control apparatus that is capable of accurately indicating the condition of a tested substance, such as the concentration of a selected solute in a selected solvent, irrespective of the presence of other factors to which a photo-electric tube is apt to respond; in other words, the invention aims to furnish a testing apparatus adapted to provide compensation for incidental factors of a variable nature, such as are liable to cause misleading response in phototubes, in order that the control operation of the apparatus be truly representative of the condition of the selected substance or substances.

With particular reference to the task of controlling the concentration of a sterilizing solution for agricultural produce, it is an object of the present invention to provide a photoelectric concentration control system, of the type described, the control operation of which is reliable no matter how great the amount of impurities suspended in the tested solution may be and how much it may vary.

It is still another object of the present invention to provide means adapted to compensate for any variation in the intensity of the light beam impinging upon the lightsensitive components of photo-electrc control systems, which result from causes other than variations of the concentration of the tested solution.

These and other objects and advantages of the present invention will become apparent from the following description and the accompanying drawings which illustrate a preferred embodiment thereof and wherein:

Fig. l is a plan view of the chassis of a practical embodiment of the present invention with the cover shown in section.

Fig. 2 is a side elevation of the control unit shown in Fig. 1.

Fig. 3 is a plan view of th lower chassis of the control unit shown in Figs. 1 and 2.

Fig. 4 is an end view of the same control unit viewed in the direction of the arrows 44 of Fig. 1 with part of the chassis removed to expose details in the interior of the instrument.

Fig. 5 is a complete wiring diagram of a photoelectric concentration-control system embodying the present invention.

Fig. 6 illustrates part of the system shown-in Fig. 5 with the symbols of certain of its components rearranged to facilitate an understanding of their functions.

Fig. 7 is a diagram illustrating the pipe system of the control unit of the invention, including the pumps and the light-transmitting cells employed therein.

Fig. 8 is a horizontal section of the photoelectric control mechanism proper taken along line 8-8 of Figs. 9 and 10.

Fig. 9 is a vertical section of the mechanism shown in Fig. 8 taken along line 9-3 thereof.

Fig. 10 is another vertical section similar to Fig. 9, taken along line Hi -l3 of Fig. 8.

Fig. 11 is a perspective view illustrating a shutter such as may be employed in the photo-electric control mechanism of the invention.

Fig. 12 is a timing diagram illustrating the duration and relative position of the operative phases of certain components of the concentra- 4 tion-control unit of the invention during two successive operative cycles thereof.

Fig. 13 is a wiring diagram illustrating one of the components employed in the control unit of the invention.

Fig. 14 is a diagram illustrating the effect of color filters in the photo-electric control system of the invention.

Fig. 15 is a diagram illustrating the phases of alternating voltages appearing on the electrodes of one of the electronic tubes employed in the system of the present invention.

Fig. 16 diagrammatically illustrates a modified embodiment of a photo-electric control apparatus constructed in accordance with my invention.

In practice, the various devices employed in accordance with the present invention to automatically control the concentration of a solution, are preferably combined into a compact portable unit which may take the form of a box or case 2!! containing an upper and a lower chassis 2| and 22, respectively, as shown in Figs. 1, 2, 3, and 4. Mounted upon the lower chassis 22 is a pump 24 which is adapted to deliver a concentrated solution of the germicidal substance from a suitable reservoir 25 into the treating tank 26 as diagrammatically indicated in Fig. 7. The pump 24 may be of the rotary type comprising two cooperating pumping units mounted upon a common shaft which is actuated by an electric motor 2?, that is arranged upon the lower chassis 22.

The lower chassis 22 of the control unit carries another pump 30 (Figs. 2, 3, and 7) which comprises two ganged pumping units 3! and 32 that have separate intake ports. A pipe line 33 connects the treating tank 26 through a transparent cell 35, to be referred to as compensating cell hereinafter, to the intake port of the pumping unit 3| (Fig. '7) so that the pump 30 may draw specimens of the treating solution through said cell 35. This cell 35 is in the form of an inverted receptacle of rectangular cross section and may be made of Pyrex glass, or any other suitable material of a transparent nature. The cell 35 is securely mounted with its open end upon a base or pedestal 3B of insulating material. such as the plastic known under the trade-name of Lucite.

The pipe line 33 (Fig. 10) communicates with the hollow interior of the cell 35 through an inlet channel 31 which terminates at the level of the upper surface of the pedestal 36, and an outlet channel 38 which is provided with an upwardly extending outlet pipe 38a that reaches closely to the ceiling of the receptacle. The bottom portion of the base 36 is preferably threaded so that the cell may be positioned by the upper chassis 2| of the control unit 20 and clamped rigidly to the upper tray 2 la which supports chassis 2!. The transparent cell 35 is encased in cylindrical metal shell or. housing 39 which may be of stainless steel. Said shell is detachably positioned by the base 36, as shown, and possessestwo rectangular windows 40 and 4| in its cylindrical wall at diametrically opposite points thereof.

A pipe (Fig. 7) connects the intake port of the second unit 32 of the testing pump 30 to a suitable reservoir, such as the bottle 45, shown in Figs. 2 and 7, which contains an indicator liquid of the type adapted to produce color formation in whatever particular sterilizing liquid may be employed. For instance, if the sterilizing liquid is an aqueous solution of sodium hypochlorite, a'concentrated solution of acidified sodium iodide may be used as indicator liquid because sodium hypochlorite and sodium iodide interact to free iodine which causes discoloration lutions; of sodium hypochloritee are; tab'e testedi because of its-tendency to reariiiy; form:yellow color in the presence; on very minute: quantities; of sodium hypochlorite, It Willi be? understood; however; that the; present: inventionis. neither limited; toanyparticular indicator liquid non. in:

fact, to any particular sterilizing solution but;

maybe employed: to control. the: concentration or kind of solution: and willwperatei;with-any substance capable-on producing color inithoe-solu tion to: be: tested-v The; pump at (Fig..- 3): s preferably or the roe tary type; with; the; rotors: of: the two. units: being;

mounted upon! a; common; shaft for; operation.=. in?

unisom and said common shaft is driven: by: anelectric: motor 41 mounted: upon thelowerchassis 22 or the controlun-it and-arranged to; operate at equal; intervals. of: predetermined, duration in a manner; to-be'described hereinafter. Both units;

of the; pumps (Figs, 3* and? 7:")- discharge: into a commons tubeorgbulb 481which isapreferably COD?" volutedi in; themannen of; an S to; promote mix-- ture: of the liquids drawnfirom-the treating tank. and tho-v indicator bottleamd thus accelerate the color-forming; interaction, on the, twocompo nents, in order that; the twoliquids be; brought; into contact; with; one another; in: pro portions best suited to: produce; feet; the two pumpunits,v may be constructed" to difl'er' in size; in: such; a manner as todraw the component liquids; in; appropriate-: quantities for optimum: performance: Thus; in the case of an aqueous solution of; sodium, hypochlorite tested; with as solution; of: sjodiurniodide,- the capacity of 1 the two pumpingunits should. be so related to? one another as t to deliver 95 parts of the; sodium hym'xchlorite-l solution into: thernixing bulb; for: every.- pa-rt ofsodium iodide:

Continued: operation of the: testing; pump; 30:

(Fig.- 7) drives the blended-liqu-ids fromzthezmixr ing bulb 48 through az pipe? line, 50 intoanother transparent cell 5|, to be referred-{toas-indicatori cell hereinafter,-, which'isrqf' a construction; similar in, all respects to; the; previously; described mpen ating? cell: 3 51 except; that; it. is; of greater depth in the, directiorrofi-thediametrically; aligned; windows; 52;.and 5:& (Figsv zi -and; 9): for reasons which: wili' presently appear; After the mixture has; passed; through the ce1l:,5|;, it may bedis charged;v throughlpipet 50w into; a. seweror any; other suitable place of;* disposal: aspindicatedi in Havingspecifio referenceto Figs. land 8;,it-

should be noted, that 1 the; described cells and;

5t are mounted sideby sideuponthePGd'estals fiaflind',35a, respectively; with thfijWiIldOWSjB; M

and" 521 5-3F of housings 39 and 39aadisposed1in diverging planes; A; suitablesourcepi lighhsuch; as. electric; lamp; 55- is located at. theinter section of: said planes-and; iS BnCaSBd; in i a? housing 51 of metal, or the like, provided witha on angularly spaced: windows: 58 and; 59 These windows arearrangedctoface the windows Mlzand: 5210p" the adjacent side of: therhousingsjfliandi 39a, respectively; through suitable tunnels fia landu 6| projecting radially fromv the housing 51, as best shown'in-Fi'gs. 8'1 Qand 10. I Orrthe other side of th'e'housings 39- and 394a said-coloring, eh-

6 of photo-electric. tubes 621andi sa is disposed; in suchv a manner that. light emitted from thelamp 56:. through the lineally alignediwindows 58%- 40, 41 andi59, 52,53 respectively, impinges upom the light-sensitive electrodes of said tubes,-- as indicated by thearrows in: Fig; 8. 'I h'e'se photo*- electric tubes are encased in: housings $1 andlu which are made-of opaque materialg-such as brass; each possessing a window 69 or 10 respectively; which communicates with: a corresponding win dow on the diverging side of the housings 3*9 01 39aithrou'gh connectin'g tunn'elslt or 1 2', respectively. In the following, the tube: 62 which: is associated with the compensating cell 35 istobe. referred to as compensating tube, while the tube 63, which isassociated with the indicator cell: 5 I:,c is to be referred to as indicator tube;

Photos-electrictubes constitute variable resistances whose values decrease with increasing: il lumination of their light-sensitive electrodes; and; in accordance with the present invention; the two"- above: described photo-tubes 62 and 63- are connected: in? series to form one branch of a; bridge circuit 13, the formed by a plurality sisters-111 15; 1 6, 11:, 18; When voltage is applied of series-connected re and 19" (Figs; 5 and 69 in the voltage difference betw-eenpoints 82 and" 33, as developed when the light-sensitive elec trodes of said tubes receivevarying degrees of illumination, are employed to control operation of" the concentrate-replenishing pump 21.

In the embodiment illustrated in thedrawingsthe power required for operating the described bridge circuit is derived from-- amain" power line (Fig; 5) represented by the leads 85' and 8H including aplug 81 for connection to anysuitabl'e source oi power, such as a light'line;

and-whichmay contain a main power control switch 88 as shown. The voltage-supplied by said line' may be raised to therequired value bya suitable input transformer 93" comprising aprimary 9| ing connected to the plates of a-full-wave-recti-- fier tube 93 output of therectifier tube is-filtered by means" of condensers ended; and stabilized by resistors 99' and I OU in combination with voltage-regulator tubes HH and M2, respectively. Dropping-re sistors l03'and' Hi4 may beprovided 'to-reduce'tlre" stabilizedD; 0.. current to the exact'valueth'at;

may be required" atthe opposite ends Bilan'dilfl of the bridgearrangement 13;

The junction 82 of the photo tubes 62 and'li'iff to the control grid "15 of is connected directly an'electrometer tube H26, the filament Hi1-of whichis placed at-point fie'betweentheresistors" 11 and 18 inthe parallel branch ofthe'bridge" circuit- 13; The anode circuit" includes a series resistor I 09; developed across saidresistor-an-d resistor-15 is applied toth'e-control grid ll tube Ill; The anode circuit of said'thyratron other branch of which istothe opposite ends so and" BI of the bridge circuit thus formed} the and 63 remainthe same or and a secondary 9'2} the latter 'b'e inthe conventional manner; The i of the tube I09 and the-voltage" 5* of a thyratron tube includes a relay H6 adapted to close the power circuit of the motor 21 for the concentrate replenishing pump 24. In Fig. 5, this power circuit is represented by a branch ||8 extending from the lead 85 of said main power line through the armature H1 of the relay HE and a motor plug 9 for the motor 21 to the other lead 85 of said main line. A lamp I20 may be shunted across the motor plug H9 to indicate visibly whenever the concentrate-replenishing pump 24 is in operation.

If the voltage supplied from the bridge circuit 13 to the control grid I05 of the electrometer tube I06 rises above a certain predetermined value, the current flow in the anode circuit of said tube places a negative bias upon the control grid of the thyratron tube I l l which renders said tube nonconductive. As a result thereof, the relay I [G in the anode circuit of said tube is unable to close the motor circuit N8 of the concentrate-replenishing pump 24. On the other hand, if the voltage supplied by the bridge circuit 13 to the control grid I85 of the electrometer tube I06 drops below said predetermined value, the current flow in the anode circuit of i said tube decreases, causing the bias applied to the control grid of the thyratron tube ill to shift in positive direction, which renders said tube conductive and permits current to flow in the anode circuit thereof.

H6 which closes the power circuit H3 of the motor 21 and initiates operation of the concentrate-replenishing pump.

In the illustrated embodiment of the present invention said critical voltage is arranged to be slightly negative and power is supplied to the bridge circuit 13 in such a manner that the vol ages at the opposite ends 86 and 8'5 of said circuit are of opposite polarity, with the voltage at point 80 adjacent to the compensating tube 62 being positive and the voltage at point 8| adjacoent to the indicator tube 63 being negative. It will be noted that the voltage at point 89 is determined by the voltage dividing network comprising resistors I03 point Si is fixed by the voltage dividing network comprising resistors N4, I9, 53, H31, 7?, 16, and 15. The values of the resistors in these two voltage dividers have been chosen to provide thyratron tube III with a negative bias when the res sistances of phototubes 62 and 83 are approximately equal. The resistances of the phototubes may be made equal by causing the same quantity of light to fall on each tube, and an adjustable shutter |2| (Figs. 8, 10, and 11) is provided for the purpose of regulating the quantity of light falling on the compensating tube, so that regardless of the exact strength of a given treating solution, or regardless of the particular depth of color produced by mixing indicator solution and the treating solution, the bridge circuit can be brought into balance by proper manual adjustment of the shutter to cause equal quantities of light to fall on the two phototubes.

This shutter |2| may take the form of a cylindrical surface |2|a of opaque material, such as stainless steel, which is rotatably arranged around the compensating tube 62 interiorly of its housing 61. This cylinder has a circumferentially extending aperture or excision [2 lb of gradually increasing vertical depth which is arranged at the axial altitude of the window ts in the tube housing 6}, as shown in Fig. 10. The cylinder |2|a is supported from an axially disposed stud |2|c which protrudes through, and is rotatably mount- This energizes the relay and 14, and the voltage at 1 ed in, the upper surface of the housing 61. A suitable locking device |'2|d may be provided to lock the protruding end of the stud l2! and to thereby retain the shutter in adjusted position.

Reverting to Fig, '7, operation of the testing pump 30 draws a specimen of the solution contained in the tank 26 in uncolored condition through the compensating cell 35, mixes it with an appropriate amount of indicator liquid in the mixing bulb 48 and then forces the mixture in colored condition through the indicator cell 5|. Now let it be assumed that the solution contained in the tank 26 is of a predetermined concentration of just the strength at which control should occur; that is to say, where any decrease in the concentration should initiate operation of the concentrate-replenishing pump and any increase in the concentration should arrest operation of said pump. To adjust the control system of the invention to this concentration level, the operator turns the shutter |2| manually until it eclipses so much of the light transmitted by the compensating cell 35 that the resistance of the compensating tube 62 is appropriately increased beyond the resistance of the indicator tube 63 as established by formation of indicator color in cell 5|, and whenever a point is reached in this adjustment at which the control system exhibits signs of instability, with the pump terminating operation when the shutter is closed further or commencing operation when the shutter is somewhat opened up again, the control mechanism of the invention has been adjusted to the selected concentration level, and the shutter may now be locked in its adjusted position.

Now let it be assumed that the solution collecting in the tank 26 contains considerable quantities of dirt, and like foreign matter in suspension which may reduce the transmission of light of the indicator cell 5| in much the same way as the color formation produced by the indicator liquid in the presence of an adequate amount of germicidal solute. As a result thereof, the resistance of the indicator tube 63 may be maintained at a level that is ordinarily indicative of an adequate degree of concentration even though the concentration of said solution may actually have dropped below the critical minimum required to sterilize fruit or vegetable.

Due to the arrangement of the invention, however, any increase in the resistance of the indicator tube 63 due to the presence of dirt in the solution, is automatically compensated for by a corresponding increase in the resistance of the compensating tube 62 because the contaminated solution passes not only through the indicator cell 5|, but also through the compensating cell 35 and reduces its ability to transmit light in the same proportion as in the case of the indicator cell 5|. Hence, whenever the tested solution is clouded or obscured by mud and the like, the resistance of both photo tubes rises proportionately so that the voltage output of the bridge circuit 13 at the junction of said tubes remains substantially the same no matter how much the specimen may be contaminated, and is influenced only by color formation resulting from the action of the indicator liquid.

For accurate operation of the described concentration control arrangement, however, it is necessary to make allowance for the fact that after its passage through the balancing cell 35 the contaminated specimen is diluted by the addition of indicator liquid. When the tested solution is thus diluted, a lesser number of dirt particles is *9 likely to be in the path .of the light beam passing through the indicator cell than obstructs the path of the light beam passing through the compensating cell 35. As ,a, result thereof, the indicator tube might register ,a lesser amount of light absorption in the indicator cell corresponding to a lesser amount of color formation 'thanis actually produced by the indicator liquid and in consequence thereof may initiate premature operation of the replenishing pump 24. In accordance with the invention, the indicator cell .5] is, therefore, of greater width in the direction of its light beam than the compensating cell, by a distance which increases the capacity of the formeras against the latter in the same proportionin which the volume of the tested solution is increased .by .the addition of the indicator liquid. As .a result thereof, substantially the same number of foreign particles will obstruct thelig'ht beam in both the indicator cell 5| and the compensating cell 35, causing the latter to provide perfect compensation for the former nomatter how strongly the tested liquid may be contaminated with foreign matter.

The described compensating arrangement provides the same effective remedy for possible inaccuracies due to fluctuations in the brilliance-of the light source 56, such as maybe caused .byirregularities in the power supply because any change in the amount .of light received by the indicator tube 63 .due to variations in the brilliance of the lamp 56 is accompanied by an equal change in the amount of light received by the compensating tube -62 so that only differences in the formation of color produced by the indicator liquid are effective :to vary the voltage output applied to the control grid v.I 05 of the ,electrometer tube I06, and thus initiate or stop operation of the concentrate-replenishing pump '2 4,.

In accordance with the invention, the described control mechanism may be provided with means to accentuate the changes in the transparency of the indicator cell, as produced by varying .degrees of indicator color formation. The indicator coloring most frequently developed ,in photoelectric concentration control apparatus is, yellow or red and its effect upon the visible light .spectrum is shown inFig. .14 wherein transmission of light is plotted against wavelength. The curve Y illustrates the light transmission of Va transparent liquid of yellow color, the amount of light passed by said liquid being represented by the area below said curve. Curve Y illustrates the transmission of light of a liquid in which greater color formation has .occured. The actual change in the amount of'light passed by the two liquids is proportionate to the ratio of the areas within the curves Y and Y. Thisratio is rather small,

in spite of a seemingly pronounced shift the position of the curves, on account of the .fact that the areas within the curves Yand Y',-difi.er only to a small extent. To increase this ratio a blue filter I22 may be interposed between the indicator cell 5| and the indicator tube 63., asshown in Figs. 8 and '9, which is arranged to reduce the transmission of the longer wavelengths .of the light. Theactual amount of light passedtothe indicator tube under .such conditions is represented by the areas within the resultants of curves Y and b and Y and b, respectively, "which .are

designated with R and R in Fig. .14. oHence in the presence of a blue filter, any change in the amount of light 'transmitted'by the indicator cell,

as represented by a shift in the .curveY to .Y, amounts to an appreciable percentage of the total amount of light received by the indicator tube efiecting a pronounced change in the control illumination supplied to said tube, so that the control mechanism of the invention will positively react even to small changes in the concentration of the controlled solution. To establish comparable conditions at the compensating tube '52, a greenofilter I 23 of appropriate transparency may be .interposedjbetween the compensating cell I35, and said tube, as shown in Figs. 1S and 10, since the light transmission characteristic of green is similar in shape and position to the resultants of yellow and blue, as illustrated by curve g in'Fig. 14.

Means are provided to operate the described testing arrangement periodically at predetermined intervals. For this purpose, .a program motor I24 is mounted upon the upper chassis H of the control unit 20 (Figs. 1, 2, and 5) and is arranged to derive power directly from the .repeatedly mentioned main line '85, 86 by means .of a branch I25 so that it will operate continuously whenever the main power switch .88 is closed. A shaft I25 driven by the program motor I24 carries three rotary cams I21, I 28., and J19, respectively, as shown in Figs. 1 and 2, and .as diagrammatically indicated in Fig. "5, and is arranged to turn at a very low rate of, say, onethird of a revolution per minute. .Each of the cams I 21, I28, and I29 is adapted .to effect temporary closure of an associated power control switch to individually energize a particular mechanism of the automatic concentrationcontrol arrangement of the invention at a predetermined time and for a predetermined duration.

Thus, the cam I21 controls the power supply circuit for the motor 41 of the testing pump .31). In the embodiment illustrated in Fig. '5, this power circuit is represented by .a lead I30 connected to the'leads and 86.01 the main line andincluding a plug I 3I for the motor 41. The .cam I2?! has a solitary depression I132 adapted to permit a switch 133 to close the power circuit I30 ,under the .force of suitable spring means (not shown) for a timedetermined by the angular width .ofisaid depression, the remainingportionof the cam=circumference being elevated to force said switch I3'3'into an open position. ,In the exemplary embodim'ent illustrated in the drawings, the cam depression I32 is shown toextend over an ,arc .of degrees. Assuming the rotary speed of the power shaft I26 to be one-third of a revolution per minute as previously indicated, this means that the testin ,pump 30 will begin to operate every seconds v for a period ,of 45 seconds .to draw a specimen of the solution from the tank "26 and .conduct it through the testing cells 35 and 5.1.

The cam I29 on .the continuously rotatingishaft I26 of the ,motor I24 is arranged to control the power supply to the source of light 56 ,of the above described photo-electric testing .arrange ment. For this purpose, the cam I29 has a solitary depression I35 of relatively short duration which is arranged to .permit a switch 136 total- .low the urge of spring means (not shown) and close apower branch I31 (Fig. 5) from the main line 85, 86 through the lamp ,5]; for a limited period of time.

The depression I3 5 in the circumference of the light control .cam I29 is of materially shorter duration than the depression 132 in the control cam L21 of the testing pump 3,0, and its angular position relative to the depression I;32is such as to delay illumination of the lamp for some time after the testing pump has commenced operation. In the exemplary embodiment illustrated and described, the depression I35 of the 1ight-control cam I29 is shown to extend over an angle of 30 degrees causing the lamp 56 to light up for a period of 15 seconds every 180 seconds, and the beginning of the depression I35 is angularly displaced relative to the beginning of the depression I32 by an angle of 60 degrees causing the testing pump 30 to operate over a period of 30 seconds, prior to illumination of the lamp 56, so as to thoroughly flush the pipe lines 33 and 45 and the cells 35 and i from any residues of a preceding test, before the actual testing operation commences.

The third of the cams mounted upon the continuously rotating power shaft I26 of the motor I24, namely cam I28, possesses a solitary depression I40 which is adapted to permit a switch I4I to temporarily close a power branch I42 from the branch line H8 and main line 86 through the coil I43 of an electromagnet I44. This electromagnet is arranged, upon excitation, to disable a spring latch I45 which tends ordinarily to retain the previously described armature I I! of the relay H6 in a position in which it closes the power circuit of the concentrate replenishing pump 24, whenever said armature is moved into this position by the described relay H6 in the anode circuit of the thyratron tube III.

The depression I 40 in the periphery of the latch-control cam I28 is of smaller duration than either of the depressions I32 and I35 in the contours of the cams I2! and i253, respectively, and

its rotary position relative to said depressions is such that its effective phase is situated completely within the effective phase of the light control cam I29. In the particular embodiment illustrated and described, the depression I40 extends over an arc of degrees corresponding to a period of only five seconds during which the electromagnet I44 prevents the latch I45 from retaining the armature II! in closing position.

Fig. 12 illustrates diagrammatically the duration and relative position of the effective phases of the above described control cams I21, I28, and I29 for one complete program cycle in the operation of the concentration control arrangement of the present invention. The numbers along the abscissa. of the diagram represent seconds, 180 I seconds being the time which the control cams require for one complete revolution. First the switch I33 (Fig. 5) drops into the depression I32 of the cam I2; and operation of the testing pump 36 commences and continues for 45 seconds, as

indicated by line a (Fig. 12). After the pump has operated for a period of 30 seconds, the switch I36 drops into the depression I of the light control cam I29 and the lamp 56 lights up rendering the photo-electric testing mechanism effective. As indicated by line b, the lamp 56 remains illuminated for a period of 15 seconds and goes out at the same time when the testing pump 30 discontinues operation.

Line 0 represents the active phase of the latchdisabling magnet I44 as determined by the depression I in the circumference of the cam I28 and indicates that the latch I is rendered ineifective over only a Very limited period which commences after commencement of the operative phase of the photo-electric testing mechanism and ends before termination thereof. After the active phase of the testing pump has come to an end and the lamp 56 has gone out, all the cam peripheries act to keep their respective program switches open for a period of at least 135 seconds, whereupon a new program cycle commences.

With the main line 85, 86 properly connected to a suitable source of power by means of the plug 81 (Fig. 5), operation of the described arrangement is initiated by manually closing the main switch 88 which starts the program motor I24. Said motor continues :to operate as long as the concentration control unit of the invention is in use, with each revolution of its power shaft I26 producing a cycle of reoccuring operations. First the switch 133 drops into the depression I32 of the cam I21 and closes the power circuit for the motor 41 of the testing pump 30 causing the latter to draw liquid from the tank 26 and conduct it :through the cells 35 and 5I. After the testing pump has operated for a time determined by the angular interval between the beginning of the depressions I32 and I35 in the cams I21 and I29, respectively, the light control switch I36 drops into the depression I35 of the cam I29 and closes the power circuit for the lamp 56 causing said lamp to light up and initiate the actual testing operation.

When the main power switch 86 was originally closed to energize the system of the invention, the rectifier tube 03 immediately drew power from the main line through the transformer 90 and supplied a filtered and stabilized D. C. voltage to the points 00 and 8| of the previously described bridge arrangement 13. With :the lamp 56 extinguished and the light-sensitive electrodes of the photo tubes 62 and 63 in complete darkness, the resistances formed by said tubes are equal but are so high as to be practically non-conductive. Under such conditions a grid leak resistor I4! (Figs. 5 and 6) of suitable design is arranged to supply a potential to the control grid of the electrometer tube I06 as will enable the anode current of said tube to block the thyratron tube I I I and maintain the relay I IS de-energized. As the lamp 56 lights up and the light emitted by said lamp impinges upon the light sensitive electrodes of the two photo tubes 62 and 63, the resistances constituted by said tubes drop instantaneously to values determined by the transparency of their respective test cells and enable the tubes to assume control of the potential supplied to the control grid of the electrometer tube I06.

Assuming the concentration of the tested solution to be sufficiently high, the voltage developed by the bridge circuit '!3 enables the anode circuit of the electrometer tube I06 to place a blocking bias upon the control grid of the thyratron tube III and render the relay II6 unable to move its armature II'l. Let it now be assumed, however, that the concentration of the solution in the treating tank drops below control-point strength and the voltage developed in consequence thereof by the photo-electric bridge circuit shifts sufficientl in negative direction to cause disappearance of the blocking bias supplied by the anode circuit of the electrometer tube I06 to the control grid of the thyratron tube III. As a result thereof, said thyratron tube fires and sends a current through the relay II6 which moves its armature II 1 into a position in which it closes the power circuit II8 of the pump 24 initiating flow of a new supply of the concentrate into the treating tank to make up for the deficit registered by the photo-electric control mechanism.

As previously explained, the armature Ill of the relay H6 is associated with a spring latch I45, as diagrammatically indicated in Fig. 5.

photo-tube resistances according ransom 13 'FIhls .latch is adapted -.to eenga e said armature i t! wheneverit is movedinto .closed position :so that the ;pump .24 may continue to supplythe concentrateinto the tank 26.after-the .lamp 56 .hasrgone out :and the;photo-electric control .cir-

cuit -|3.has.been restored to its condition of rest which the relay .I I6 isde-energized. .In the .illustrated embodiment, a period of 135 seconds will elapse after the .lamp .56 .hassgone out and .after the testing ,pump 30 has ceased :to operate, .beforethe'testing pump control switch 133 drops again into the depression 4-32 of its-control cam i527 and initiates anew cycle in theoperationof the testing. mechanism. Again the testing ,pump

-.30 drawsliquid from the tank and flushes the .piping of the control unit e for a period .of .seconds until the lamp 56 lights to adjust the to the intensity .of the color formation produced by the indicator fliquidin the new specimen. If the test indicates that the concentration of the solution in the .tank has meanwhile risen above the control point, the .controlrelay 1 l6 .for said pump .remains inactive; but the concentrate supply pump will continue to operate since the'la'tch continues to retain the armature ll] in closing position. IH'owever, soon after the "test lamp 5.6 vThasilit up, the switch Ml drops into the .depres ISlOIl 1140 of its program cam in and closes the power "line "2 of the latch disabling electromagnet "I'M which withdraws theilatch M5 from the power-control armature H1 provided armature H?! was closed andthat current wasffiowing throughbranch l't8. "Infthe absence of any attraction from its control relay H6 the armature I ['1 will now return to 'itsnormally open position 'in which thepowerasupply 'for the motor of the concentrate-replenishing pump "is interrupted, causing the supply of concentrate to the tank 16 ?to cease.

The depression MO in the program cam T28 is .oI smaller width than either of the depressi'ons 'in'the program cams I21 and I29, and the period over which the latch-disabling magnet PM is energized, is'there'fore .veryshort and isarranged to 'end before termination of the illumination period of "the test lamp '56, as diagrammatically illustrated in Fig. .12. Therefore, whenever a photo-electric test, performed while the concentraite replenishing "pump is in operation, indi- "cates that the concentration in the tank is "still 'subnormal, the resultant activation of the con- 'trol relay H6 maintains T'lihB armature 1H fin "closed 'con'dit'ion 'during the short period, when the latch M5 isdisa'b'led. Hence, upon termination of its ine'fiective period, said latch may again "engage said armature 1 "f1 and thus insure uninterrupted operation of the concentrate-replenishing pump 24 for at least "another cycle "in the operationof the program shaft-1'26.

The arrangement of the present invention includes automatic means to guard against inappropriately continuing "operation of the concentrate-replenishing pump 24, such "as would raise theconcentration of the treating solution in tank '26 to a degree that may 'deleteriously affect the texture, tasteandappearance of the treated produce, and which may be caused by failureof the latch disabling electro-rnagnet M4 to withdraw the latch 14 5 from the pump- -control armature 11-1 'or by a breakdown in the photo-electric control circuit 13, or for any other cause of faulty operation which tends to maintain the concentrate replenishing pump operating. For thispurpose, (the power circuit 14:8 0f

.rnctor'fliorthe replenishing pump includes :a device 150 adapted \to :interrupt :said circuit vwhenever said pump has operated longer'thana predetermined .gperiod --of time, and to maintain said circuit :in interrupted condition until .it is broken at an additional point exteriorly of said devicelindicating that the-situation. hasbeen no- .ticediand attended to byopening thexmain :power switch 88. .-A device that may be arranged .to perform in-this manner-is-an instrument know-n under the vname of Cramer Time-Delay Instantaneous Re-Set-Relay and, in thesfcllowing, the construction of such a device will be'briefiy described. It should :be understood, however, that thisdevice well known in the art-and it lsthemannerin which it is fitted into the'organization of .thedescribedcontrol unit, ratherthan itsconstruction, which forms part of .the present invention.

Referring to .Figs. .5 and .13, a device .of the type referred to, comprises a safety switch iii which :is placed into the power circuit -H.8 vofthe concentrate-rep]enishing .pump and .is normally .lield in closed position .by spring means .(not shown) .Inaddition, the device comprisesa con- .trol .motor [52 which is shunted across the .Ithemotor plug .l [9 of the concentrate-replenishing .pump through -.a .normally closed switch I153. .A normally disengaged clutch 154 Iisarlra-nged to establish operating connection between said .con'trolmo'tor 152 and a control arm [55 (indicated in broken lines) whenever said clutch (is engaged by operation of an electromagnet [56 which is shunted across the ,power lines and 86 through switch H 1. "The control arm T55 is arranged to open'both saidswitches 'I5l and 1'53 whenever .it jhas been advanced by the 'motorl'52 over a predetermined distance, but is normally held in an initial position removed from said switches by a'suitable spring means (not shown).

Whenever the photo -electrii'c control system l3 energ'izes "the "relay lffi which'mcves the armaiture H 1 into closed position and thus initiates operation of the motor 2"! of the concentrate replenishingpump; power will also fl-owlthroug-h the control motor 152 causing said motor to comtmence'operation. "In addition, actuation of the armature H7 initiates flow .o'fpower through the shuntline which contains the electi e-magnet [516 and "thus cause-s engagement of the clutch 1'54.

establishes driving connection between the operating motor 152 and the control arm [55 so thatthe latter will move toward the switches [51 and 153. Thus, whenever the armature 1H1 keeps the circuit H8 closed beyond a predetermine'dfperiod of Itime, said arm [5 5 reaches the switches 1'51 and I53 and throws them open. terminates 'op'er "tion of the concentratereplenishing pump 24 and, in addition, terminates .op- 'eration of :the control motor I52. However, the clutch control electroemagnet 1.56 remains .energi'zed as long as the armature M! remains .in closed position and, therefore,.maintains the control arm I55 in .rigi'd connection with the .motor [52 so that said arm .is unable to return :to its initial .position :under the force of its restore spring and, theretore, continues to keiep the switches 451 and .153 .in open positions, :Since the source eofgpoiwer rfOI electric-magnet PM is removed :when switch .151 is opened, the latch T45 is :held inoperative armature H will not open. iHence,theel-ectro-magnet l 'ifiis de-energized only when the manually operable main power switch 88 is opened "which indicates that the abnormal condition of the apparatus has been noticed and is being properly attended to. The clutch I54 is disengaged by the opening of the main switch 38 permitting instantaneous r.- turn of the control arm I55 to its initial position which, in turn, permits restoration of the switches II and I53 to their normally closed positions, and thus reconditions the described safety device for a new operational cycle. The described device I56 may be provided with a manually adjustable setting lever I51 (Fig. l) to pre-set the period of time that may elapse before its control arm I55 opens the safety switch I5I.

The described arrangement positively prevents uncontrolled operation or" the concentrate-replenishing pump, such as is liable to deliver excessive amounts of the concentrate into the treating tank and thus effectively protects the treated produce from any injury due to excessive con centration of the treating solution. Since it may be necessary, however, to have the concentratereplenishing pump operate uninterrupted for an extended period of time at the beginning of a sterilizing process, to prepare the proper solution in the treating tank, a manually operable shunt switch I58 (Fig. 5) is provided to connect the motor plug IIS directly across the main power line 85 and 86 and permit operation of the concentrate-replenishing pump for any desired period of time without interference from any of the described control or safety mechanisms.

Furthermore, the safety switch I5I may be arranged to energize a red lamp I59 (Figs. 2, 5, and 13) or some other signalling means, when opened to interrupt the power circuit of the concentrate replenishing pump, so as to warn personnel in attendance that the control unit 26 is out of operation.

It will be understood that a concentration control unit of the type described would be completely disorganized and may come to lasting harm if either of the light-transmitting cells 35 or 5| should develop a leak. In such a case, continued operation of the testing pump 30 would cause the escaping liquid to spread over the upper chassis and seep into the interior of the apparatus which may seriously damage the components thereof and is liable to cause dangerous short circuits of its electric wiring connections. The arrangement of the present invention, therefore, comprises means adapted instantaneously to stop operation of both the testing and the replenishing pumps, if ever a leak should develop in one of the light-transmitting cells.

For this purpose, a ring or collar I60 of conductive material, such as stainless steel, is ari ranged near the top of each of the pedestals 36 and 36a. These collars are of such size as to be situated exteriorly of the transparent cells but are sufficiently smaller in diameter than the metal housings 39 and 39a to be radially spaced therefrom, as shown in Figs. 8, 9, and 10. While the metal shells 36 and 39a are connected to ground, as diagrammatically indicated in Fig. 5, a suitable conductor I6I extending through the interior of the pedestal (Figs. 9 and connects the collar I66 of each of said cells directly to the control grid I62 of a thyratron tube I63, the anode circuit of which includes arelay I64 that is adapted, upon excitation, to simultaneously open two normally closed switches I65 and I66 situated in the power lines I58 and I of the replenishing pump 24 and the testing pump 36, respectively.

Normally, the control grid I62 of the thyratron tube I63 is supplied with a biasing potential adapted to block said tube and prevent current flow in the anode circuit thereof so that the relay I64 is unable to open the switches I65 and I66. However, as soon as one of the cells 35 or 5I develops a leak, the escaping solution establishes conductive connection between the collar :60 and the cell housing 39 or 39a of the defective cell so that the control grid I62 of the thyratron tube I63 is efiectively connected to ground. This abolishes the blocking potential normally applied to said grid and causes said tube I63 to fire. The resultant current flow in the anode circuit of said tube energizes the relay I64 which opens the switches I65 and I66 and thus interrupts the power supply for both the testing pump and the concentrate-replenishing pump. Hence, said pumps are unable to operate until the damage has been repaired and there is no danger for the testing pump to force liquid through the leak in the defective cell over and into the control unit or for the photo-electric control circuit to become disorganized and cause the replenishing pump to deliver excessive amounts of the concentrate into the treating tank 26.

The safety switch I66 in the power circuit I30 of the testing pump 30 may be arranged to close a shunt line I61 through a warning light I68, whenever it is opened by the relay I64 in the manner described above, to indicate to attending personnel that the testing pump is out of commission and requires expert, attention.

In the particular embodiment illustrated in Fig. 5 the blocking potential for the control grid I62 of the thyratron tube I63 is derived directly from the heater I16 of said tube. For this purpose, the arrangement is such that one side of said heater is grounded to the cathode I1I of the tube while its other side is connected to the control grid I52 through a conductor I13 which may include the resistor I14 and I15, and the heater is powered by an alternating voltage of opposite phase to the voltage applied to the anode I16. Thus, whenever a positive voltage appears at the anode I16 of the thyratron tube, the conductor I13 supplies a negative voltage to the control grid I62, as illustrated in Fig. 15, wherein curve a represents the alternating voltage appearing between the anode I16 and the cathode I1I while curve It represents the oppositely alternating voltage supplied by the ungrounded side of the heater I10. To prevent accidental firing of the tube at those intersections of curves (1 and h, where the anode voltage builds rapidly up in positive direction while the negative bias supplied by the heater is still very small, means may be provided in the form of a condenser I11 shunted across the resistor I15 to somewhat advance the alternating phases of the voltage supplied to the control grid, as illustrated by curve 9 which indicates that the biasing voltage on the control grid I62 drops to an appreciable negative value before a positive potential appears at the anode of said tube.

Means may also be provided to automatically terminate operation of both the testing pump and the replenishing pump whenever the supply of indicator liquid in the reservoir 46 is exhausted because continued operation of the control unit 20 without an adequate supply of indicator liquid would falsely register insufficient concentration of the treating solution, due to lack of color formation in the indicator cell 5|, and would thus cause untimely operation of the concentrate replenishing pump. For this purpose, the previously described conductor I13 which delivers the 17 biasing potential to. the control grid I62 of the thyratron tube. [03. may be, interrupted with its severed ends located at 'a predetermined level in the indicator bottle, 46, as'diagrammatically indicated at I80 in Fig. 5."

As long as the. severed ends of the conductor I13 are immersed in the indicator liquid, they are conductively connected so that the control grid I62 of the thyra tron tube I03 remains prop-.- erly biased to block said tube. However, as soon as the supply in the. indicator reservoir drops below the level of the severed ends of conductor 113 the biasing connection between the heater and grid of the thyratron tube IE3 is disrupted and the blocking bias on the control grid I62 of said tube disappears. As a result thereof, the tube fires and energizes the relay I02 which opens the safety switches I65 and I06 of both the testing and the replenishing pumps and illuminates the warning light I68 in the manner previously described. The. pumps are kept out, of operation until the supply of indicator. liquid in the bottle 40 ha been sufiiciently replenished to, cover the severed ends of the conductor I13 which reestablishes the blocking bias at the control grid of the, thyratron tube I153 and thus inactivates the relay I In consequence thereof, the safety switches I65 and 56 may follow the urgency of suitable restoring springs (not shown) and close the power circuits for the testing and replenishing pumps and the control unit may resume its normal operation.

The manner of operation and the manipulation of the control "unit of the invention will be apparent from the above given explanations. Briefly, the intake and discharge pipes of the concentrate replenishing pump 24 are connected to the concentrate reservoir 25 and the treating tank 20, respectively, and the intake pipe of the testing pump unit 3|, is, likewise, connected to the treating tank 26 while the intake pipe of the unit 32 is connected to the indicator liquid bottle 46. The main power plu 81 is then connected to some suitable source of power, such as a light line, and the switch 88 is closed, whereupon the unit commences operation. To condition the unit for op ration with a particular solution, the treating tank should first be filled with said solution in a state of concentration representa tive of the desired control point, and during the operative phases of the testing pump 30 and the lamp 56, the operator manipulates the adjustable shutter I2I of the compensating photo-tube 62 until an unstable condition of the concentrate-.- replenishing pump 24 indicates that the voltage developed by the photo-electric control circuit, 13 with an indicator color formation as produced by the exemplary concentration of the solution is of just the right magnitude and character to prevent operation of the concentrate replenish. ing pump but will initiate such operation should the color formation diminish. From then on-. ward control of the solution in the treating tank may be left entirely to the unit 20 which will maintain it within its proper limits, no matter how much the transparency of the liquid may vary due to contamination by dirt or other .im-v purities. All that an attendant has to do, is to glance occasionally at the various lights of the unit. If the lamp I2!) is illuminated, he is informed that the concentration of the solution has dropped below the control point and is being raised to its proper level by operation of the concentrate replenishin pump. If the lamp I59 lights up, it tells him: that the control unit has Photo-electric control apparatus Tubes 62, 63 Photo-tubes type 441.

Tube 93 F'ull wave rectifier tube type 1 17Z6-GT.

Tubes I01 I 02-" Voltage regulator tube type Tube I06 Electrometer tube type X41.

Tube I I l Thyratron tube type 502A.

115 v. 60 cycle primary 9|. Transformer 230 v. 60 cycle secondary 92.

' 6.3 v. 60 cycle secondary 92 Condenser 94, 95. 16 mfd.

Condenser 96 8 mfd. Condenser 91 .001 mfd. Condenser 98 10 mfd. Resistor 14 1300 ohms. Resistor 15 100 ohms. Resistor 16 l ohms. Resistor 11 450 ohms. Resistor 18 150 ohms. Resistor 19 1850 ohms. Resistors 99, I 00- 15 00 ohms. Resistor I03 6200 ohms Resistor IM 4800 ohms. Resistor I09 150,000 ohms. Resistor II2 10,000 ohms. Resistor H3 0.5 megohm. Resistor H4 500 ohms. Resistor I41 100. megohms. Relay II6 Struthers-Dunn type 51AXX10 latching relay. Leak detector mechanism Tube I63 Thyratron tube type 502A.

1 15 v. 60 cycle primary I9l.

Transfurmer t 115v. 60 cycle secondary I 92.

Condenser I11 .01 mfd.

Co d n ,0 mf

Resistor l1L 3 megohms.

Resistor I--- 1 megohm.

Resistor I 94 2 megohms.

R si o 95-.----,- 5 0 o ms- Relay I64 Struthers Dunn type l AAlfi. rel y. Voltage of main Th Ph be-e ec ric e n ap a tu of t Present nve ti n ma b em t n a on r re a i ns other ha th of Solute nd o ent Thus His 10 i us m i e emo iment i he p otolec ri te appara wh h i arrang d. o nd c e au m t a l he respectively, with I The surface to be provided with a coat of varnish is represented by a sheet of cardboard 210 which is moved past the two photo-tubes in the direction from the balancing tube 20l to the indicator tube 202, as shown by the arrow 2| 1. A suitable source of light, such as the lamp 2l2, is positioned intermediately of the two photo-tubes and is provided with a pair of adjustable windows, indicated at 2 l4 and 215, respectively, which are arranged to direct a pair of diverging light beams against the surface 2H) in such a manner that said beams are reflected onto the light-sensitive electrodes of the balancing tube and the indicator tube, respectively, as shown by the arrows drawn in broken lines.

Arranged intermediately of the points at which the two light beams impinge upon the surface 2I0 is a spray nozzle 220 through which a. layer of paint or varnish 225 is applied to said moving surface 218. In case the arrangement is such that the output volume of the spray nozzle 220 is manually controlled, a suitable indicator device 222, such as a galvanometer, a vacuum tube voltmeter or a self-balancing potentiometer, is connected between the junction points 223 and 22d of the photo-tubes EM, 292 and the resistors 2514, 295, respectively, and is provided with a calibrated scale 225 that may bear the notations High and Low.

In practical operation the amount of light transmitted to the light-sensitive electrode of the indicator tube 232 varies according to the thickness of the coating formed on the surface 2H1, that is to say, it decreases as said thickness increases and increases as it decreases. The resultant changes in the resistance of the indicator tube cause corresponding shifts in the voltage developed between the control points 223 and 22d of the bridge circuit 283 which move the needle in the indicator device 222 from an initially established standard position to positions indicating greater or lesser thickness, as the case may be. To guide the operator of the spray nozzle, the above described notations High and Low on the scale 225 of the indicator device may be provided at points representative of critical lower or upper limits for the thickness of the coat 22 I.

Let it now be assumed that the travelling surface 2H3 to which the varnish is applied, changes its hue and becomes darker. Since this reduces the amount of light reflected to the indicator tube 282 and thus causes an increase in the resistance of said tube, such a change in the appearance of the surface 2H3 would ordinarily cause a shift in the voltage output of the bridge circuit 253 that incorrectly indicates an increase in the thickness of the coat 22l formed on the surface 2H). In the described arrangement, however, such a change in the appearance of the surface produces a corresponding decrease in the amount of light reflected to the compensating tube 25! and, hence, increases the resistance of said tube accordingly so that the voltage output of the bridge circuit 203 is maintained at its previous level. The same effective compensation occurs whenever the surface 210 changes to a brighter hue in that a greater amount of light is reflected to the compensating tube as well as the indicator tube. Thus, the needle of the indicator device 222 will not respond to any changes in the hue or color of the treated surface but will change its position only when the thickness of the coating varies, enabling the operator to re-adjust the output volume of the spray nozzle or regulate the 20 speed at which the surface travels past said 'noz= zle in such a manner as to maintain the thickness of the coating within the required limits.

It will be understood that automatic mechanisms similar in nature to those employed in conneotion with the previously described concentration control unit may be provided to actuate the volume control means of the spray nozzle 220 or regulate the speed of travel of the surface 2l0 in response to the varying control voltages devel oped by the photo-electric testing circuit illus trated in Fig. 16.

While I have described a preferred apparatus for carrying out the present invention, it will be understood that its constructional details may be varied without departing from the spirit and scope of the claims appended hereto.

Having thus described the present invention, what I claim as new and desire to protect by Letters Patent is:

l. A concentration control unit for solutions including replenishing means adapted to increase the concentration of a controlled solution, a photo-electric testing mechanism having an activating lamp, sampling mechanism arranged to conduct specimens of said solution through said testing mechanism, said testing mechanism being arranged to develop varying voltages according to the concentration of said specimens upon illumination of said lamp, a relay adapted to activate said replenishing means in response to predetermined ones of said voltages, latching means to retain said relay in said activating position upon disappearance of said voltages, means adapted to disable said latching means, and cyclically operable means to periodically activate said sampling mechanism, said lamp and said latch-disabling means.

2. A concentration control unit for solutions, including replenishing means adapted to increase the concentration of a controlled solution, photoelectric testing mechanism having an activating lamp, sampling mechanism arranged to conduct specimens of said solution through said testing mechanism, said testing mechanism being arranged upon illumination of said lamp to develop different voltages according to the concentration of said specimens, a relay adapted to activate said replenishing means in response to predeter- .mined ones of said voltages, latching means adapted to retain said relay in activating position upon disappearance of said voltages, means adapted to disable said latching means, cyclically operable means to periodically activate said sampling mechanism for a limited period of time,

cyclically operable means to periodically activate said lamp for a period of shorter duration than the operative phase of said sampling mechanism, and cyclically operable means to periodically activate said latch-disabling means for a period of shorter duration than, and situated wholly within, the operative phase of said lamp.

. 3. A concentration control unit for solutions contained in a tank, comprising a replenishing pump adapted to deliver a concentrate of said solution into saidtank and having a normally open power circuit, photo-electric control mechanism having an activating lamp, a sampling pump arranged to conduct specimens of said solution through said testing mechanism, said testing mechanism being arranged to develop different voltages according to the concentration of said specimens, a relay responsive to selected ones of said voltages indicative of substandard concentration of said specimens to close said power circuit for said replenishing pump, a latch adapted to retain said relay in said closing position upon disappearance of said voltages, an electromagnet adapted to disable said latch, and cyclically operable means arranged to periodically activate said sampling pump, said lamp and said electromagnet in the sequence named over overlapping periods of unequal duration.

4. A concentration control system for solutions comprising a replenishing pump having a normally open power circuit, a photo-electric testing arrangement having a lamp adapted to activate said arrangement upon illumination thereof and a sampling pump arranged to conduct specimens of a controlled solution through said photo-electric testing arrangement, said arrangement being adapted upon activation to develop difierent control voltages according to the concentration of said specimens, cyclically operable means to activate said sampling pump and illuminate said lamp at periodic intervals to develop said control voltages for limited periods of time, mechanism responsive to selected ones of said control voltages to close said power circuit for said replenishing pump, latching means effective to retain said mechanism in closing position upon disappearance of said voltages, cyclically operable means briefly effective during reappearance of said control voltages to disable said latching means and permit said mechanism to interrupt said power circuit whenever said reappearing voltages differ from said selected voltages.

5. A testing arrangement for liquids comprising a hollow transparent cell, a pump arranged to conduct liquid through said cell, a power circuit for said pump, a relay operable to open said power circuit, a circuit including a pair of relatively spaced conductive elements situated adjacent to said cell exteriorly thereof, said circuit being effective upon collection of liquid in the space between said elements to activate said relay.

6. Arrangement according to claim wherein one of said elements is a metal housing enveloping said transparent cell and the other one of said elements is an annular metal collar situated within said housing and surrounding said cell near the bottom thereof.

7. In a testing arrangement having a transparent hollow cell, a pump arranged to conduct liquid through said cell and a power circuit for said pump, mechanism for suspending operation of said pump in the event of leakage from said cell comprising an electronic tube having a control grid, said grid being ordinarily biased to block said tube, a relay situated in the anode circuit of said tube, and operable to interrupt said pump circuit, and means adapted upon escape of liquid from said cell to effectively connect said grid to ground.

8. A testing arrangement for liquids including a hollow transparent cell, a metal housing encasing said cell, said housing being connected to ground, a pump arranged to conduct liquid through said cell, a power circuit for said pump, an electronic tube having a control grid, said grid being ordinarily biased to block said tube, a relay situated in the anode circuit of said tube and operable to interrupt said power circuit, and a conductor leading from said control grid to a 22 point adjacent to, but out of contact with, said housing and near the bottom of said cell, in order that liquid leaking from said cell may electrically bridge the gap between said conductor and said housing and in this manner connect the control grid of said electronic tube to ground.

9. Arrangement according to claim 8 including a warning light, adapted to be illuminated by operation of said relay, to visibly indicate leakage from said cell and consequent suspension of said pump.

10. In a testing arrangement for solutions having a transparent hollow cell, a reservoir containing indicator liquid, a pump arranged to mix specimens of a tested solution with measured quantities of said indicator liquid and conduct said specimens through said cell, and a power circuit for said pump, mechanism for suspending operation of said pump in the event of leakage from said cell, comprising a thyratron tube having an anode, a control grid, a cathode, and a heater, one side of said heater being grounded to said cathode, means for applying an alternating voltage to said anode, means for applying an alternating voltage of opposite phase to said heater, and a first conductor connecting the ungrounded side of said heater to said control grid to supply a blocking potential to said grid, a relay situated in the anode circuit of said tube and operable to open the power circuit for said pump, and an ordinarily interrupted second conductor arranged in uninterrupted condition to connect said control grid to ground, the interruption of said second conductor being located closely adjacent to said transparent cell near the bottom thereof to be conductively bridged by any liquid that may escape from said cell.

11. Arrangement according to claim 10 wherein said first conductor is likewise interrupted with the severed ends thereof situated at a predetermined level within the reservoir containing said indicator liquid in order to suspend operation of said pump whenever the supply of said indicator liquid drops below said predetermined level.

WESLEY N. LINDSAY.

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